Custom mood themes are a paid feature, but super cool! You just need to make about 15 different icons as they repeat to similar moods but you can make up to 115 I think to cover every mood. Oh though if you are going to do the full 115 you may need to look up a tutorial on how to use the Admin Console to automate it as it gets a bit laborious!

Here's the manual mood theme editor/creator page https://www.dreamwidth.org/manage/moodthemes